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To follow up and enhance the question on powering MCU with parasitc 1-Wire interface.

How to ensure proper power on reset of MCU in such situation?

For example this two standard method of generating power on reset may fail:

a) resistor/capacitor delay generated reset -> during power rump up, for extensive period of time data line can be low (for example due to data transmission) or pulled up only by significant resistance. This may slow MCU local supply rise time to the level that will render RC delay useless.

b) global, board level reset may not work as most probably will be removed before local MCU supply will stabilize as the "master" side of 1-wire will provide power only after reset is removed (not to mention that routing reset line defy point of using 1-Wire interface)?

What kind of precautions needs to be taken in such situations? Should MCU be equipped with brownout detection? Is that enough?

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1 Answers1

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As you've noticed, RC on the reset pin is not going to work when you have very slow voltage rise times.

Built-in brownout detection may work, but read the microprocessor's datasheet carefully to see if there is a minimum rise time on the supply voltage.

If you are not sure built-in brownout detection will work, you can use a "voltage supervisor" chip. The basic supervisor is a three-terminal device that connects to power and ground, and pulls the output low when the power voltage is below the setpoint. Connect it to reset and you're good to go. You can buy these in a variety of voltages and turn-on delays.

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  • Power management ICs are very good at this and can be a very important part of a resilient device. – Kortuk Dec 01 '10 at 01:55